研究者業績
基本情報
- 所属
- 国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 助教総合研究大学院大学 宇宙観測科学講座 飛翔体天文学分野 助教
- 学位
- 博士(理学)(1998年3月 京都大学)修士(理学)(1995年3月 京都大学)
- 研究者番号
- 80342624
- ORCID ID
https://orcid.org/0000-0002-9099-5755- J-GLOBAL ID
- 202001011170717781
- researchmap会員ID
- R000011919
論文
248-
Journal of Astronomical Telescopes, Instruments, and Systems 11(04) 2025年12月18日
-
Publications of the Astronomical Society of Japan 2025年11月25日Abstract A high-resolution X-ray spectroscopic observation was made of the RS CVn-type binary star HR 1099 using the Resolve instrument onboard XRISM for its calibration purposes. During the $\sim$400 ks telescope time covering 1.5 binary orbit, a flare lasting for $\sim$100 ks was observed with a released X-ray radiation energy of ${\sim }10^{34}$ erg, making it the first stellar flare ever observed with an X-ray microcalorimeter spectrometer. The flare peak count rate is 6.4 times higher than that in quiescence and is distinguished clearly in time thanks to the long telescope time. Many emission lines were detected in the 1.7–10 keV range both in the flare and quiescent phases. Using the high spectral resolution of Resolve in the Fe K band (6.5–7.0 keV), we resolved the inner-shell lines of Fe xix–xxiv as well as the outer-shell lines of Fe xxv–xxvi. These lines have peaks in the contribution functions at different temperatures over a wide range, allowing us to construct the differential emission measure (DEM) distribution over the electron temperature of 1–10 keV (roughly 10–100 MK) based only on Fe lines, thus without an assumption of the elemental abundance. The reconstructed DEM has a bimodal distribution, and only the hotter component increased during the flare. The elemental abundance was derived based on the DEM distribution thus constructed. A significant abundance increase was observed during the flare for Ca and Fe, which are some of the elements with the lowest first ionization potential among those analyzed, but not for Si, S, and Ar. This behavior is seen in some giant solar flares and the present result is a clear example in stellar flares.
-
The Astrophysical Journal 994(1) 37-37 2025年11月13日Abstract The balloon-borne hard X-ray polarimetry mission XL-Calibur observed the black hole X-ray binary (BHXRB) Cygnus X-1 (Cyg X-1) during its nearly 6 day long-duration balloon flight from Sweden to Canada in 2024 July. The XL-Calibur observations allowed us to derive the most precise constraints to date of the polarization degree (PD) and polarization angle (PA) of the hard X-ray emission from a BHXRB. XL-Calibur observed Cyg X-1 in the hard state and measured a ∼19–64 keV PD of ( )% (equivalent to an upper limit, at the 99% level, of 11.1%) at a PA of −28° ± 17°, with an 8.7% chance probability of detecting larger PDs than the one observed, given an unpolarized signal. The XL-Calibur results are thus comparable to the 2–8 keV PD and PA found by Imaging X-ray Polarimetry Explorer (IXPE), with a similar agreement between the hard X-ray PA and the radio jet direction. We also discuss the implications of our polarization measurements in the context of models describing the origin of the broadband X-ray and γ -ray emission, to which XL-Calibur provides independent constraints on any proposed emission modeling.
-
UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIV 51-51 2025年9月18日
-
Optics for EUV, X-Ray, and Gamma-Ray Astronomy XII 19-19 2025年9月18日
-
Journal of Astronomical Telescopes, Instruments, and Systems 11(04) 2025年8月21日 査読有り筆頭著者責任著者
-
Publications of the Astronomical Society of Japan 77(Supplement_1) S96-S106 2025年6月17日Abstract The Galactic Center region was observed with the X-Ray Imaging and Spectroscopy Mission (XRISM) X-ray observatory during the performance verification phase in 2024 and a point-like X-ray source was detected with the X-ray imager Xtend at a position of $(\alpha , \delta )_{\rm J2000.0}=({17^{\rm h}46^{\rm m}10{_{.}^{\rm s } }8}, {-29^{\circ}00^{\prime }21^{\prime \prime } })$, which is thus named XRISM J174610.8-290021. This source was bright in February to March and showed time variations in count rate by more than one order of magnitude in one week. The 2–10 keV X-ray luminosity was ${\sim }10^{35}$ erg s$^{-1}$ for the assumed distance of 8 kpc. However, after six months, it was below the detection limit. We found a hint of periodicity of 1537 s from timing analysis. The XRISM/Xtend spectrum has emission lines from helium-like iron (Fe xxv–He$\alpha$) at 6.7 keV and hydrogen-like iron (Fe xxvi–Ly$\alpha$) at 6.97 keV; their intensity ratio is unusual with the latter being four times stronger than the former. If the emission is of thermal origin, the ionization temperature estimated from the iron-line intensity ratio is $\sim$30 keV, which is inconsistent with the electron temperature estimated from the thermal bremsstrahlung, $\sim$7 keV. Spectral models of magnetic cataclysmic variables, which are often seen in the Galactic Center in this luminosity range, are found to fail to reproduce the obtained spectrum. By contrast, we found that the spectrum is well reproduced with the models of low-mass X-ray binaries containing a neutron star plus two narrow Gaussian lines. We consider that the source is intrinsically bright reaching $10^{37}$ erg s$^{-1}$, but is blocked from direct view due to a high inclination and only the scattered emission is visible. The photo-ionized plasma above the accretion disk with an ionization parameter of ${\sim }10^{5}$ may explain the unusual iron line ratio. We further discuss the potential contribution of point sources of the type of XRISM J174610.8-290021 to the diffuse Galactic Center X-ray emission.
-
Monthly Notices of the Royal Astronomical Society: Letters 540(1) L34-L40 2025年3月19日ABSTRACT We report measurements of the linear polarization degree (PD) and angle (PA) for hard X-ray emission from the Crab pulsar and wind nebula. Measurements were made with the XL-Calibur ($\sim$15–80 keV) balloon-borne Compton-scattering polarimeter in July 2024. The polarization parameters are determined using a Bayesian analysis of Stokes parameters obtained from X-ray scattering angles. Well-constrained ($\sim 8.5\sigma$) results are obtained for the polarization of the $\sim$19–64 keV signal integrated over all pulsar phases: PD = (25.1$\pm$2.9) per cent and PA = (129.8$\pm 3.2)^\circ$. In the off-pulse (nebula-dominated) phase range, the PD is constrained at $\sim 4.5\sigma$ and is compatible with the phase-integrated result. The PA of the nebular hard X-ray emission aligns with that measured by IXPE in the 2–8 keV band for the toroidal inner region of the pulsar wind nebula, where the hard X-rays predominantly originate. For the main pulsar peak, PD = (32.8$^{+18.2}_{-28.5}$) per cent and PA = (156.0 $\pm$ 21.7)$^\circ$, while for the second peak (inter-pulse), PD = (0.0$^{+33.6}_{-0.0}$) per cent and PA = (154.5 $\pm$ 34.5)$^\circ$. A low level of polarization in the pulsar peaks likely does not favour emission originating from the inner regions of the pulsar magnetosphere. Discriminating between Crab pulsar emission models will require deeper observations, e.g. with a satellite-borne hard X-ray polarimeter.
-
Nature 638(8050) 365-369 2025年2月12日 査読有り
-
Publications of the Astronomical Society of Japan 77(1) L1-L8 2024年12月26日 査読有りAbstract Sagittarius A East is a supernova remnant with a unique surrounding environment, as it is located in the immediate vicinity of the supermassive black hole at the Galactic center, Sagittarius A$^{*}$. The X-ray emission of the remnant is suspected to show features of overionized plasma, which would require peculiar evolutionary paths. We report on the first observation of Sagittarius A East with the X-Ray Imaging and Spectroscopy Mission (XRISM). Equipped with a combination of a high-resolution microcalorimeter spectrometer and a large field-of-view CCD imager, we for the first time resolved the Fe xxv K-shell lines into fine structure lines and measured the forbidden-to-resonance intensity ratio to be $1.39 \pm 0.12$, which strongly suggests the presence of overionized plasma. We obtained a reliable constraint on the ionization temperature just before the transition into the overionization state, of $\gt\! 4\:$keV. The recombination timescale was constrained to be $\lt\! 8 \times 10^{11} \:$cm$^{-3}\:$s. The small velocity dispersion of $109 \pm 6\:$km$\:$s$^{-1}$ indicates a low Fe ion temperature $\lt\! 8\:$keV and a small expansion velocity $\lt\! 200\:$km$\:$s$^{-1}$. The high initial ionization temperature and small recombination timescale suggest that either rapid cooling of the plasma via adiabatic expansion from dense circumstellar material or intense photoionization by Sagittarius A$^{*}$ in the past may have triggered the overionization.
-
The Astrophysical Journal Letters 977(2) L34-L34 2024年12月11日 査読有りAbstract The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this Letter, we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer, which provides unprecedented spectral resolution and sensitivity in the 2–10 keV band. We detect multiple kinematic and ionization components in absorption and emission whose superposition leads to complex line profiles, including strong P Cygni profiles on resonance lines. The prominent Fe xxv Heα and Fe xxvi Lyα emission complexes are clearly resolved into their characteristic fine-structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ∼−500–600 km s−1. We show that the wind decomposes naturally into a relatively smooth and large-scale component, perhaps associated with the background wind itself, plus a turbulent, denser structure located close to the compact object in its orbit.
-
Publications of the Astronomical Society of Japan 76(6) 1186-1201 2024年10月10日 査読有りAbstract We present an initial analysis of the X-Ray Imaging and Spectroscopy Mission (XRISM) first-light observation of the supernova remnant (SNR) N 132D in the Large Magellanic Cloud. The Resolve microcalorimeter has obtained the first high-resolution spectrum in the 1.6–10 keV band, which contains K-shell emission lines of Si, S, Ar, Ca, and Fe. We find that the Si and S lines are relatively narrow, with a broadening represented by a Gaussian-like velocity dispersion of $\sigma _v \sim 450$ km s$^{-1}$. However, the Fe He$\alpha$ lines are substantially broadened with $\sigma _v \sim 1670$ km s$^{-1}$. This broadening can be explained by a combination of the thermal Doppler effect due to the high ion temperature and the kinematic Doppler effect due to the SNR expansion. Assuming that the Fe He$\alpha$ emission originates predominantly from the supernova ejecta, we estimate the reverse shock velocity at the time when the bulk of the Fe ejecta were shock heated to be $-1000 \lesssim V_{\rm rs}$ (km s$^{-1}$) $\lesssim 3300$ (in the observer frame). We also find that Fe Ly$\alpha$ emission is redshifted with a bulk velocity of $\sim 890$ km s$^{-1}$, substantially larger than the radial velocity of the local interstellar medium surrounding N 132D. These results demonstrate that high-resolution X-ray spectroscopy is capable of providing constraints on the evolutionary stage, geometry, and velocity distribution of SNRs.
-
The Astrophysical Journal Letters 973(1) L25-L25 2024年9月1日 査読有りAbstract We present an analysis of the first two XRISM/Resolve spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 4151, obtained in 2023 December. Our work focuses on the nature of the narrow Fe K α emission line at 6.4 keV, the strongest and most common X-ray line observed in AGN. The total line is found to consist of three components. Even the narrowest component of the line is resolved with evident Fe K α,1 (6.404 keV) and K α,2 (6.391 keV) contributions in a 2:1 flux ratio, fully consistent with neutral gas with negligible bulk velocity. Subject to the limitations of our models, the narrowest and intermediate-width components are consistent with emission from optically thin gas, suggesting that they arise in a disk atmosphere and/or wind. Modeling the three line components in terms of Keplerian broadening, they are readily associated with (1) the inner wall of the “torus,” (2) the innermost optical “broad-line region” (or “X-ray BLR”), and (3) a region with a radius of r ≃ 100 GM/c 2 that may signal a warp in the accretion disk. Viable alternative explanations of the broadest component include a fast-wind component and/or scattering; however, we find evidence of variability in the narrow Fe K α line complex on timescales consistent with small radii. The best-fit models are statistically superior to simple Voigt functions, but when fit with Voigt profiles the time-averaged lines are consistent with a projected velocity broadening of FWHM . Overall, the resolution and sensitivity of XRISM show that the narrow Fe K line in AGN is an effective probe of all key parts of the accretion flow, as it is currently understood. We discuss the implications of these findings for our understanding of AGN accretion, future studies with XRISM, and X-ray-based black hole mass measurements.
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 55-55 2024年8月22日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 53-53 2024年8月22日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 75-75 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 232-232 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 56-56 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 58-58 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 236-236 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 224-224 2024年8月21日
-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 59-59 2024年8月21日
-
Astroparticle Physics 158 102944-102944 2024年6月 査読有り
-
Publications of the Astronomical Society of Japan 2024年2月9日 査読有りAbstract We develop a new deconvolution method to recover the precise Crab Nebula image taken by the Hitomi HXT, suppressing the artifact due to the bright Crab pulsar. We extend the Richardson–Lucy method, introducing two components corresponding to the nebula and pulsar with regularization for smoothness and flux, respectively, and performing simultaneous deconvolution of multi-pulse-phase images. The structures, including the torus and jets, seen in the deconvolved nebula image at the lowest energy band of 3.6–15 keV appear consistent with those identified in the high-resolution Chandra X-ray image. Above 15 keV, we confirm NuSTAR’s findings that the nebula size decreases in higher energy bands. We find that the north-east side of the nebula is fainter in higher energy bands. Our deconvolution method is applicable for any telescope images of faint diffuse objects containing a bright point source.
-
SPACE TELESCOPES AND INSTRUMENTATION 2024: ULTRAVIOLET TO GAMMA RAY, PT 1 13093 2024年
-
Monthly Notices of the Royal Astronomical Society 527(3) 7121-7135 2023年11月27日 査読有りABSTRACT We analyse the XMM–Newton RGS spectra of Wolf–Rayet (WR) 140, an archetype long-period eccentric WR+O colliding wind binary. We evaluate the spectra of O and Fe emission lines and find that the plasmas emitting these lines have the largest approaching velocities with the largest velocity dispersions between phases 0.935 and 0.968 where the inferior conjunction of the O star occurs. This behaviour is the same as that of the Ne line-emission plasma presented in our previous paper. We perform a diagnosis of the electron number density ne using the He-like triplet lines of O and Ne-like Fe–L lines. The former results in a conservative upper limit of ne ≲ 1010–1012 cm−3 on the O line-emission site, while the latter cannot impose any constraint on the Fe line-emission site because of statistical limitations. We calculate the line-of-sight velocity and its dispersion separately along the shock cone. By comparing the observed and calculated line-of-sight velocities, we update the distance of the Ne line-emission site from the stagnation point. By assuming radiative cooling of the Ne line-emission plasma using the observed temperature and the local stellar wind density, we estimate that the line-emission site extends along the shock cone by at most ±58 per cent (phase 0.816) of the distance from the stagnation point. In this framework, the excess of the observed velocity dispersion over that calculated is ascribed to turbulence in the hot-shocked plasma at earlier orbital phases of 0.816, 0.912, and 0.935, with the largest velocity dispersion of 340-630 km s−1 at phase 0.912.
-
Optics for EUV, X-Ray, and Gamma-Ray Astronomy XI 2023年10月5日
-
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1048 167975-167975 2023年3月 査読有り
-
Journal of Low Temperature Physics 209(5-6) 971-979 2022年12月 査読有り
-
Journal of Astronomical Telescopes, Instruments, and Systems 8(04) 2022年10月22日 査読有り
-
Monthly Notices of the Royal Astronomical Society 2022年5月10日<jats:title>Abstract</jats:title> <jats:p>We analyze a series of XMM-Newton RGS data of the binary Wolf-Rayet star WR140 that encompasses one entire orbit. We find that the RGS detects X-rays from optically-thin thermal plasma only during orbital phases when the companion O star is on the near side of the WR star. Although such X-rays are believed to be emitted from the shock cone formed through collision of the stellar winds, temperature and density profiles of the plasma along the cone have not been measured observationally. We find that the temperature of the plasma producing Ne emission lines is 0.4-0.8 keV, using the intensity ratio of Kα lines from He-like and H-like Ne. We also find, at orbital phases 0.816 and 0.912, that the electron number density in the Ne line-emission site is approximately 1012 cm−3 from the observed intensity ratios f/r and i/r of the He-like triplet. We calculated the shock cone shape analytically, and identify the distance of the Ne line-emission site from the shock stagnation point to be 0.9-8.9× 1013 cm using the observed ratio of the line-of-sight velocity and its dispersion. This means that we will be able to obtain the temperature and density profiles along the shock cone with emission lines from other elements. We find that the photo-excitation rate by the O star is only 1.3-16.4 per cent of that of the collisional excitation at orbital phase 0.816. This implies that our assumption that the plasma is collisionally excited is reasonable, at least at this orbital phase.</jats:p>
-
Publications of the Astronomical Society of Japan 74(2) 477-487 2022年3月21日 査読有りAbstract We report on the results of our simultaneous observations of three large stellar flares with soft X-rays (SXRs) and an Hα emission line from two binary systems of RS CVn type. The energies released in the X-ray and Hα emissions during the flares were 1036–1038 and 1035–1037 erg, respectively. This renders the set of the observations as the first successful simultaneous X-ray/Hα observations of the stellar flares with energies above 1035 erg; although the coverage of the Hα observations was limited, with $\sim\! 10\%$ of the e-folding time in the decay phase of the flares, that of the SXR ones was complete. Combining the obtained physical parameters and those in literature for solar and stellar flares, we obtained a good proportional relation between the emitted energies of X-ray and Hα emissions for a flare energy range of 1029–1038 erg. The ratio of the Hα-line to bolometric X-ray emissions was ∼0.1, where the latter was estimated by converting the observed SXR emission to that in the 0.1–100 keV band according to the best-fitting thin thermal model. We also found that the e-folding times of the SXR and Hα light curves in the decaying phase of a flare are in agreement for a time range of 1–104 s. Even very large stellar flares with energies of six orders of magnitude larger than the most energetic solar flares follow the same scaling relationships with solar and much less energetic stellar flares. This fact suggests that their physical parameters can be estimated on the basis of the known physics of solar and stellar flares.
-
Proceedings of SPIE - The International Society for Optical Engineering 12181 2022年
-
Publications of the Astronomical Society of Japan 73(5) 1418-1428 2021年10月4日 査読有り<title>Abstract</title> We present our analysis of the Suzaku data of SS Cygni (SS Cyg) from 2005 both in quiescence and outburst. A fluorescent iron Kα line bears significant information about the geometry of an X-ray-emitting hot plasma and a cold reflector, such as the surfaces of the white dwarf (WD) and the accretion disk (AD). Our reflection simulation has revealed that the X-ray-emitting hot plasma is located either very close to the WD surface in the boundary layer (BL), with an upper limit radial position of &lt;1.004 times the white dwarf radius (RWD), or near the entrance of the BL where the optically thick AD is truncated at a distance of 1.14–1.27 RWD for the assumed WD mass of 1.19 M⊙ in quiescence. In the latter configuration, the plasma torus is located just above the inner edge of the AD. The result suggests that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the BL. The matter probably expands precipitously at the entrance of the BL and leaves the disk plane to reach a height comparable to the radial distance of the plasma torus from the center of the WD. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface. In addition, the plasma distributes above the disk like coronae, as suggested by a previous study, and the 90% upper limit of the coronae radial position is 1.2 RWD.
-
Journal of Astronomical Telescopes, Instruments, and Systems 7(2) 2021年4月 査読有り
-
Journal of Geophysical Research: Space Physics 126(4) 2021年4月 査読有り
-
The Astrophysical Journal 910(1) 25-25 2021年3月1日 査読有り<jats:title>Abstract</jats:title> <jats:p>We report that the RS CVn–type star GT Mus (HR 4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. We detected 11 flares from GT Mus in 8 yr of observations with the Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. The detected flare peak luminosities were 1–4 × 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup> in the 2.0–20.0 keV band for its distance of 109.6 pc. Our timing analysis showed long durations (<jats:italic>τ</jats:italic> <jats:sub>r</jats:sub> + <jats:italic>τ</jats:italic> <jats:sub>d</jats:sub>) of 2–6 days with long decay times (<jats:italic>τ</jats:italic> <jats:sub>d</jats:sub>) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band were in the range of 1–11 × 10<jats:sup>38</jats:sup> erg, which are at the upper end of the observed stellar flare. The released energies during the whole duration were in the range of 2–13 × 10<jats:sup>38</jats:sup> erg in the same band. We carried out X-ray follow-up observations for one of the 11 flares with the Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 10<jats:sup>12</jats:sup> cm (or 60 <jats:italic>R</jats:italic> <jats:sub>☉</jats:sub>). The electron density is derived to be 1 × 10<jats:sup>10</jats:sup> cm<jats:sup>−3</jats:sup>, which is consistent with the typical value of solar and stellar flares (10<jats:sup>10–13</jats:sup> cm<jats:sup>−3</jats:sup>). The ratio of the cooling timescales between radiative (<jats:italic>τ</jats:italic> <jats:sub>rad</jats:sub>) and conductive (<jats:italic>τ</jats:italic> <jats:sub>cond</jats:sub>) cooling is estimated to be <jats:italic>τ</jats:italic> <jats:sub>rad</jats:sub> ∼ 0.1 <jats:italic>τ</jats:italic> <jats:sub>cond</jats:sub> from the temperature; thus, radiative cooling was dominant in this flare.</jats:p>
-
Astroparticle Physics 126 102529-102529 2021年3月 査読有り
-
Publications of the Astronomical Society of Japan 73(1) 143-153 2021年2月5日 査読有り<title>Abstract</title> We present our analysis of the Suzaku data of U Geminorum (U Gem) from 2012 both in quiescence and outburst. Unlike SS Cygni (SS Cyg), the hard X-ray flux of U Gem is known to increase at times of optical outburst. A sophisticated spectral model and reliable distance estimate now reveal that this can be attributed to the fact that the mass accretion rate onto the white dwarf (WD) does not exceed the critical rate that causes the optically thin to thick transition of the boundary layer. From comparison of the X-ray and optical light curves, the X-ray outburst peak seems to be retarded by 2.1 ± 0.5 d, although there remains uncertainty in the X-ray peak identification, due to short data coverage. The larger delay than SS Cyg (0.9–1.4 d) also supports the lower accretion rate in U Gem. A fluorescent iron 6.4 keV emission line bears significant information about the geometry of the X-ray-emitting hot plasma and the accretion disk (AD) that reflects the hard X-ray emission. Our reflection simulation has shown that the optically thick AD is truncated at a distance of 1.20–1.25 times the white dwarf radius (RWD) in quiescence, and the accreting matter in the disk turns into the optically thin hard-X-ray-emitting plasma at this radius. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface, although disk truncation can take place in the region of &lt;1.012 RWD. From the profile of the 6.4 keV line, we have also discovered that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the boundary layer at the disk truncation radius. This is consistent with the fact that the hard X-ray spectra of dwarf novae, in general, can be well represented with the cooling flow model.
-
Journal of Astronomical Telescopes, Instruments, and Systems 7(01) 2021年1月6日 査読有り
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2021年1月4日 筆頭著者責任著者
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月30日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月14日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月13日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 11444 2020年12月13日
-
ASTROPHYSICAL JOURNAL 893(1) 2020年4月 査読有り
-
ASTROPHYSICAL JOURNAL 891(2) 2020年3月 査読有り
MISC
93講演・口頭発表等
6-
44th COSPAR Scientific Assembly 2022年
-
nuclear burning in massive stars – towards the formation of binary black holes – 2021年7月28日
-
Space Telescopes and Instrumentation 2020: Ultraviolet to Gamma Ray 2020年12月19日
担当経験のある科目(授業)
6-
2023年9月 - 2024年3月
-
2021年4月 - 2022年3月宇宙理学概論(オムニパス) (総合研究大学院大学)
-
2019年10月 - 2020年3月宇宙理学概論(オムニパス) (総合研究大学院大学)
-
2009年10月 - 2010年3月応用物理学講義 (中央大学)
-
2009年4月 - 2009年9月宇宙物理学講義 (中央大学)
共同研究・競争的資金等の研究課題
12-
日本学術振興会 科学研究費助成事業 2023年4月 - 2027年3月
-
日本学術振興会 科学研究費助成事業 2022年4月 - 2025年3月
-
日本学術振興会 科学研究費助成事業 基盤研究(B) 2022年4月 - 2025年3月
-
日本学術振興会 科学研究費助成事業 基盤研究(A) 2020年4月 - 2023年3月
-
日本学術振興会 科学研究費助成事業 挑戦的研究(萌芽) 2019年6月 - 2022年3月
